1. Field of the Invention
The present invention relates to an integral melt-out metal core assembly for overmolding and production of molded plastic components. More specifically the present invention relates to forming several metallic rings into a core assembly for use in forming a plastic injection molded component; and in particular this invention is applicable to the manufacture of multi-blade plastic turbine rotors for automatic transmissions.
2. Description of the Related Art
Melt-out metal alloy parts of intricate complexities are made for overmolding with plastic to form plastic components that have internal or external undercuts and hollowed-out areas which could not be manufactured by known demolding techniques of state-of-the-art toolmaking principles. Melt-out alloy cores are used for manufacturing such products as: propellers, turbines, stators, pump wheels, impellers and other circular arrayed parts which have to be molded as a one piece construction, but have heavily overlapping blades or channels which make molding by conventional means impossible. One approach to developing a manufacturing process for use in making an injection molded plastic component such as a turbine is proposed in U.S. Pat. No. 5,173,237, which discloses use of a plurality of metallic core segments, typically one for each blade or vane, to form the required internal or external geometry of the finished plastic part. The single core segments are assembled into a ring shape prior to loading the core assembly into a mold mounted on a plastic molding machine. The prior art requires that each core segment be manually inserted into the core assembly or where feasible automates the assembly of the single segments by a robotic unit. It is both time consuming and very costly to have to first produce the relative high number of single core segments ranging typically from seven to thirty, and then to assemble the core segments into a ring shaped multiple core segment assembly. Furthermore, a significant tolerance build-up in the multiple core segment assembly leads inevitably to poor finished part quality due to dimensional inadequacies and poor surface finish caused by excessive flash from poor fitting segments of the core assembly. Thus, there is a need in the art for a method of making multi-segment plastic components which takes into consideration the need for high quality and dimensionally accurate parts, in a simple and efficient manner.